When you’re in an assignment, on a quest, undertaking an investigation, or just out on an expedition, press the [Options]/[Menu] button, scroll to the “Quest” tab, and pick the option “Fire SOS Flare” to earn this shiny new trophy/achievement. You’ll have to advance the story to the assignment The Great Jagras Hunt before you can send an SOS Flare, however, and keep in mind that the game is somewhat restrictive about when you can do this on assignments. In most assignments, you can’t send out an SOS Flare until you’ve witness certain cutscenes - almost exclusively scenes introducing you to new monsters.